The present disclosure relates to plastic reinforcing articles. Strips and cellular confinement systems (CCSs) are made from polymer compositions optimized for use in geotechnical application. In many applications, the reinforcement is provided with minimal friction and normal stresses with the soil or alike. The result is limited reinforcement, and high level of undesired deformation in the strip itself and between it and the confined soil.
Plastic articles, reinforcing geotechnical-reinforced materials (GRMs), especially CCSs, are used to increase the load bearing capacity, stability and erosion resistance of GRMs which are supported by the CCSs.
CCSs comprise a plurality of high density polyethylene (HDPE) or medium density polyethylene (MDPE) strips in a characteristic honeycomb-like three-dimensional system. The strips are welded to each other at discrete locations to achieve this system. Geotechnical materials can be reinforced, confined and stabilized within or by CCSs. The surfaces of the CCS are sometimes embossed to increase friction with GRM and decrease relative movement between CCS and GRM.
The mechanical properties of GRM-filled CCSs are a composite phenomenon wherein the stiffness and rigidity is provided by the pressed infill (the GRM) and the plastic CCS cell walls provide mechanical continuity and dynamic load bearing. The normal stress applied by GRM on CCS walls, is the sum of hydrostatic pressure provided by GRM height and the compression of the GRM. The normal stress is responsible for the load bearing of the CCS wall. The higher the normal stress, the better the friction between the CCS wall and GRM. Anytime the load transfer between these two components is breached, due to cell wall creep, rupture or irreversible deformation, the filled CCSs lose their integrity and cannot provide the required structural strength, dimensional stability and stiffness. Moreover, in shallow GRMs and close to surface of the geotechnical material layer, wherein normal stress of GRM on CCS walls is low or sometimes approximately zero, relative low forces cause deformations that harm the integrity, leading to structural failure, erosion of GRM and finally disintegration of the CCS-GRM composite system. The combination of shallow GRMS and slope, has further negative effects, since compaction of GRM into CCS cells, is difficult in slopes.
The term “HDPE” refers hereinafter to a polyethylene characterized by density of greater than 0.940 g/cm3. The term medium density polyethylene (MDPE) refers to a polyethylene characterized by density of greater than 0.925 g/cm3 to 0.940 g/cm3.
Current commercially available CCSs are generally made solely from HDPE or MDPE. CCS cell walls made from HDPE are stiff in the vertical direction, they maintain some flexibility in the horizontal direction, they are dimensionally stable, resist creep relatively well, and have sufficient stiffness when the cells are still empty and GRM is then provided, generally by dumping the GRM onto the CCS, then packing the cells within the CCS. If the CCS wall is too flexible, it will collapse during installation in the field, especially during the filling and condensing of GRM in the CCS cells. However, HDPE is relatively rigid; it has a 1% secant flexural modulus according to ASTM D790 of about 950 megapascals (MPa). The GRM is filled into the CCS, and compacted by mechanical press or alike. The composite system comprising the CCS and the compressed GRM inside, behaves as a structural unit, when loaded, vibrated or deformed. The friction between the CCS walls and the GRM is the load bearing mechanism and is a key property in the CCS long term integrity and functionality.
Usually, when a geotechnical construction is provided based on CCS and GRM, the uppermost layers, those that are on the surface down to about 1 meter, are most subjected to erosion due to the lowest normal pressure and highest rain and wind erosion, combined with vibrations, human activity and extreme climate conditions. Normal pressure is defined hereinafter as the sum of hydrostatic pressure of GRM plus compaction pressure.
Flat or embossed CCS provides relatively good cohesion and friction with GRM. Usually, when a flat HDPE strip having a thickness of 1 to 1.2 mm is in contact with shallow GRM, such as sand or graded crushed stone that provides relative moderate-low normal pressure in the range of 0.05 to 0.4 Atmosphere, the deformation created in the strip during pullout test is less than 1.2 mm for every 1 meter embedded length. This level of deformation is low enough to guarantee dimensional stability of GRM filled CCS comprising smooth or embossed walls.
The major problem of CCSs is the poor drainage between cells and the limited volume in cell so that plants grow poorly in CCS. In order to solve these important issues, CCS comprising apertures in walls are commercially available and also described in the patent literature, e.g., U.S. Pat. No. 6,395,372 which discloses a perforated cellular confinement system. Typical perforated CCS comprises about 10 to 15% of walls surface area occupied by perforation. The perforation lowers the stiffness of the CCS, so that higher deformations are observed, especially at low normal pressures or stresses. For example, a flat HDPE strip having thickness of 1 to 1.2 mm, perforated by 10 mm diameter circular apertures at 10 to 15% of its surface area, in contact with GRM, such as sand or graded crushed stone that provides relative moderate-low normal pressure, in the range of 0.05 to 0.6 Atmosphere, has a deformation created in the strip during the pullout test of about 3 to 8 mm for every 1 meter length. This level of deformation is relatively high, and it is not possible to guarantee dimensional stability of the perforated CCS-GRM composite system s.
It is thus a long felt need to provide perforated CCS with improved friction with GRM at low normal pressure in the range of about 0.05 to 0.6 Atmosphere ospheres, and with lower tendency to deform under loads provided by vibrations, human activity, erosion and drainage. The improved CCS are especially useful for confinement and reinforcement of GRM in the uppermost layers in the geotechnical system, wherein normal stresses on CCS wall are low or even zero.